Salon asks how far Bush's AWOL violation will contribute to his demise, but in the meantime here is a nice summary paragraph of the issue.

Salon.com News | Bush's missing year: "The story emerged in 2000 when the Boston Globe's Walter Robinson, after combing through 160 pages of military documents and interviewing Bush's former commanders, reported that Bush's flying career came to an abrupt and unexplained end in the spring of 1972 when he asked for, and was inexplicably granted, a transfer to a paper-pushing Guard unit in Alabama. During this time Bush worked on the Senate campaign of a friend of his father's. With his six-year Guard commitment, Bush was obligated to serve through 1973. But according to his own discharge papers, there is no record that he did any training after May 1972. Indeed, there is no record that Bush performed any Guard service in Alabama at all. In 2000, a group of veterans offered a $3,500 reward for anyone who could confirm Bush's Alabama Guard service. Of the estimated 600 to 700 Guardsmen who were in Bush's unit, not a single person came forward. "